In the first blast, a bus bomb went off on one of Tel Aviv's busiest thoroughfares, reportedly injuring 12 people, sparking panic and sending black smoke billowing through the air.
A few hours later, two Israelis were killed and two were injured in a roadside explosion along Israel's border with Gaza Strip, military sources said.
Police sources, speaking on condition of anonymity, said the blast occurred near a crossing point as the Israelis were attempting to dismantle the device.
The latest violence came as efforts to implement the U.S. peace plan lurched from hope to uncertainty. Egypt called off plans to host the summit at the prompting of Israel, which said it was frustrated with what it called Palestinian leader Yasser Arafat's intransigence.
Though many Arabs denounced U.S. President Bill Clinton's peace proposals--which call for deep and painful concessions from both Israelis and Palestinians--it won support from key Mideast power brokers Egypt and Saudi Arabia.
Both sides had expressed reservations about the U.S. proposals. However, Israeli Prime Minister Ehud Barak accepted the plan as a basis for further talks, while Palestinians sharply contested it.
``If Arafat wants to be the stubborn one, then let him,'' Israeli Cabinet minister Yuli Tamir told army radio. ``He's missing a historic opportunity... The Palestinian people will pay a heavy price for this.''
Egyptian leaders have repeatedly said the peace process is the only way for the Israelis and Palestinians to work out their differences. Egyptian
Foreign Minister Amr Moussa on Thursday praised Clinton's efforts and added: ``In order to activate President Clinton's initiative, it seems it needs some time.''
``These issues should be discussed with our Arab brothers,'' Arafat told reporters in the Gaza Strip.
Late Wednesday the Palestinians sent the Clinton administration a letter detailing misgivings on 24 separate points in the proposal, news reports said. A senior Palestinian official said the objections were serious enough to amount to a rejection of the plan, but the State Department said it was still awaiting a formal Palestinian response.
There was no immediate claim of responsibility for the Tel Aviv explosion, which news reports said injured 12 people, one seriously. Hospital officials confirmed 10 people hurt.
Barak vowed to track down those responsible, but also saying such attacks would not deter his government from peace efforts.
``We will continue our determined war against terror, and as in the past, will get at those who carry out these acts,'' he said in a statement. ``The criminal attack won't crack our determination to bring real security through an end to the conflict and to bloodshed in the area.''
During the past three months of violence, Palestinian militants have claimed responsibility for two bombings inside Israel, one in a Jerusalem market and the other in the northern town of Hadera. Since late September, fighting by Israeli troops and Palestinians in the West Bank, Gaza Strip and east Jerusalem has killed nearly 350 people, most of them Palestinians.
The Islamic militant group Hamas disclaimed knowledge of the Tel Aviv blast, but said Israel could expect more of the same.
``For us it's doesn't matter who is responsible ... as long as he is part of this intefadeh,'' Hamas spokesman Ismail Abu Shanab told The Associated Press. ``It's the Palestinian people who are determined to continue this intefadeh.''
Media reports said Israel sought the cancellation after Palestinians sharply questioned the U.S. proposals.
But Israel, too, was digging in its heels on some elements of the plan. Danny Yatom, Barak's security adviser, suggested Israel was having second thoughts about the Temple Mount, the holiest site in Judaism. Palestinians revere the site as Haram as-Sharif--the Noble Sanctuary--and demand sovereignty over it.
``In regard to the Temple Mount, there is still a lot more that needs to be said,'' Yatom told Israel radio.
Barak told his Cabinet he would not sign any agreement transferring sovereignty over the Temple Mount to the Palestinians--even though his foreign minister, Shlomo Ben-Ami, had said after last week's Washington talks that Israel was prepared to take such a step.
The prime minister, who faces an election challenge in less than six weeks from veteran right-wing politician Ariel Sharon, had come in for a storm of criticism over the planned concession, from across the political spectrum.
Parliament speaker Avraham Burg told Israel radio that shared control of the hilltop site would be the best solution.
The Palestinians, meanwhile, appeared most opposed to requirements they scale back demands for the return of millions of refugees to their homes in Israel.
Both sides requested a number of clarifications of the U.S. plan.